create sql tables (#40)

Co-authored-by: Eduard S <eduard@iden3.io>

db/utils.go

@@ -0,0 +1,78 @@
+package db
+
+import (
+	"encoding/base64"
+	"fmt"
+	"math/big"
+	"reflect"
+	"strings"
+
+	"github.com/russross/meddler"
+)
+
+// InitMeddler registers tags to be used to read/write from SQL DBs using meddler
+func InitMeddler() {
+	meddler.Register("bigint", BigIntMeddler{})
+}
+
+// BulkInsert performs a bulk insert with a single statement into the specified table.  Example:
+// `db.BulkInsert(myDB, "INSERT INTO block (eth_block_num, timestamp, hash) VALUES %s", blocks[:])`
+// Note that all the columns must be specified in the query, and they must be in the same order as in the table.
+func BulkInsert(db meddler.DB, q string, args interface{}) error {
+	arrayValue := reflect.ValueOf(args)
+	arrayLen := arrayValue.Len()
+	valueStrings := make([]string, 0, arrayLen)
+	var arglist = make([]interface{}, 0)
+	for i := 0; i < arrayLen; i++ {
+		arg := arrayValue.Index(i).Addr().Interface()
+		elemArglist, err := meddler.Default.Values(arg, true)
+		if err != nil {
+			return err
+		}
+		arglist = append(arglist, elemArglist...)
+		value := "("
+		for j := 0; j < len(elemArglist); j++ {
+			value += fmt.Sprintf("$%d, ", i*len(elemArglist)+j+1)
+		}
+		value = value[:len(value)-2] + ")"
+		valueStrings = append(valueStrings, value)
+	}
+	stmt := fmt.Sprintf(q, strings.Join(valueStrings, ","))
+	_, err := db.Exec(stmt, arglist...)
+	return err
+}
+
+// BigIntMeddler encodes or decodes the field value to or from JSON
+type BigIntMeddler struct{}
+
+// PreRead is called before a Scan operation for fields that have the BigIntMeddler
+func (b BigIntMeddler) PreRead(fieldAddr interface{}) (scanTarget interface{}, err error) {
+	// give a pointer to a byte buffer to grab the raw data
+	return new(string), nil
+}
+
+// PostRead is called after a Scan operation for fields that have the BigIntMeddler
+func (b BigIntMeddler) PostRead(fieldPtr, scanTarget interface{}) error {
+	ptr := scanTarget.(*string)
+	if ptr == nil {
+		return fmt.Errorf("BigIntMeddler.PostRead: nil pointer")
+	}
+
+	data, err := base64.StdEncoding.DecodeString(*ptr)
+	if err != nil {
+		return fmt.Errorf("big.Int decode error: %v", err)
+	}
+	field := fieldPtr.(**big.Int)
+	*field = new(big.Int).SetBytes(data)
+
+	return nil
+}
+
+// PreWrite is called before an Insert or Update operation for fields that have the BigIntMeddler
+func (b BigIntMeddler) PreWrite(fieldPtr interface{}) (saveValue interface{}, err error) {
+	field := fieldPtr.(*big.Int)
+
+	str := base64.StdEncoding.EncodeToString(field.Bytes())
+
+	return str, nil
+}